Superchargers Use More Fuel
Engineers realized during the early 1920′s that the use of a pumping cylinder could, and did, result in the charge being introduced to the combustion chamber of an engine at a pressure higher than that of the normal atmosphere. Therefore more mixture could be available to provide more power per firing stroke. This point had not been overlooked by designers of four stroke engines and supercharging, as it was known, was experimented with as far back as the turn of the century, although with reciprocating pumps. Ten years later rotary pumps were being tried but none of these reached production cars until at least the mid 1920s, when superchargers were first used on production cars such as the new Rolls Royce. The supercharger, in producing greater power from a given engine size, has its disadvantages. These are mainly in the much greater amount of heat generated in the engine and in the carry over of the oil needed to lubricate the blower, besides the power needed for driving it. Just as the air is heated by the compression within the cylinder, so it is heated by compression in a supercharger. Although these pumps increased the pressure by only a few pounds per square inch, the increased heat and the additional final pressure within the combustion chamber required either an improvement in the anti detonation properties of the fuel or a lowering of the engine compression ratio. Broadly speaking, two types of compressor were used. One was the Centric or Cozette, which had rotors with radially sliding vanes working within an eccentric casing. The other was the Roots type, originally designed on a much larger scale by Jones in 1859 for ventilating coal mines, which had two intermeshing rotors of figure eight shape. The Roots type supercharger was used mounted vertically in front of the engine of the 1924 new Mercedes Benz 15/70/100, which later developed into the legendary Mercedes S Class and SSK from 1929 to 1934. Unlike other cars such as Lea Francis, Frazer-Nash and A.C., which compressed the fuel/air mixture, the Mercedes blew into the carburettor. Moreover, in the interests of fuel economy and engine life, the blower was driven through a disc clutch which was engaged only when the throttle pedal was fully depressed. With the advent of wartime fuel shortages and low octane ratings, the supercharger was largely abandoned except for a few firms which fitted them as extras to standard engines. Larger capacity engines to produce the required higher power were more the fashion. A more recent form of supercharging is the use of the turbo blower in which a turbine, driven by the gases on their way down the exhaust system, powers a centrifugal fan or blower, thus aiding the mixture on its way between the carburettor and inlet ports. In 1971, Ralph Broad developed a system in which the use of a turbo charger was rendered optional by a switch on the facia and a solenoid operated changeover valve passed unpressurized air to the carburettor when extra power was not wanted.
~admin
Tags: mercedes s class, new mercedes benz, new rolls royce
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